**Question:** Which one of the following is the primary defect in Pierre Robbin syndrome?

A. Hypoplastic lungs
B. Congenital diaphragmatic hernia
C. Hypoplastic kidneys
D. Hypoplastic liver

**Core Concept:** Pierre Robbin syndrome is a congenital disorder characterized by three main features:

1. Obstructive uropathy (renal, ureteral, or bladder obstruction)
2. Hypoplastic kidneys
3. Congenital diaphragmatic hernia (CDH)

**Why the Correct Answer is Right:** The primary defect in Pierre Robbin syndrome is the combination of hypoplastic kidneys and congenital diaphragmatic hernia (CDH). The hypoplastic kidneys result from impaired renal development due to renal agenesis or hypoplasia, leading to obstructive uropathy. Congenital diaphragmatic hernia is a structural defect in the diaphragm that allows the abdominal organs to herniate into the thoracic cavity, which further exacerbates the respiratory distress in neonates.

**Why Each Wrong Option is Incorrect:**

A. Hypoplastic lungs (Congenital diaphragmatic hernia): Although respiratory distress is a significant feature of Pierre Robbin syndrome, it is not the primary defect. Hypoplastic lungs are a consequence of CDH, not the primary cause.

B. Hypoplastic liver: Similar to option A, hypoplastic liver is a consequence of CDH, not the primary defect.

C. Hypoplastic kidneys: As mentioned above, hypoplastic kidneys are the result of obstructive uropathy, not a primary defect.

**Clinical Pearl:** Pierre Robbin syndrome is a critical diagnosis for pediatricians and neonatologists due to its association with high neonatal mortality and morbidity. Early recognition and management can significantly improve outcomes, including respiratory support, renal replacement therapy, and surgical correction for CDH.